North Star MDS-A-O User Manual page 31

DP has shared use. During stepping operations, OP=0
specifies a step out and OP=l specifies a step in.
During write operations, write procompensation is
invoked if and only if DP=l.
ST controls the level of the head step signal to the disk
dr ives.
os is the drive select field, encoded as follows
0=no drive selected
l=drive 1 selected
2=drive 2 selected
4=drive 3 selected
8=drive 4 selected
CASE 3
Controller Commands
Perform a disk controller command. The commands are
specified by the B low order address bits.
OM The OM field controls what gets multiplexed onto the
01 bus during the command.
l=A-status
2=B-status
3=C-status
4=Read data (may enter wait state)
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CC Command code.
0=no operation
l=reset sector flag
2=disarm interrupt
3=arm interrupt
4=set body (diagnostic)
5=turn on drive motors
6=begin write
7=reset controller, de-select drives, stop motors
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North Star MICRO-DISK System